If I remember correctly, it was mid to late 80's that Shimano brought out the Biopace chainrings. Those rings are not round like almost all chain rings are but rather slightly elliptical which was supposed to give the rider a more efficient peddling motion. They did not go over well and were dropped only a few years later. Some people really liked them but I developed some knee pain that I had never experienced before and changed them out to standard round rings, and my discomfort went away almost immediately. But as I said, some including yourself may luv em'